Neurodegeneration is an increasing public health issue and remains an unsolved biomedical challenge. Genetic discoveries have provided news avenues for investigating the molecular mechanisms of several neurodegenerative diseases. Recently, a hexanucleotide repeat expansion in a noncoding region of the C9orf72 gene was linked to the neurodegenerative disease amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). ALS is characterized by loss of motor neurons, and the C9orf72 mutation represents the most common genetic cause of both familial and sporadic ALS. FTD is characterized by degeneration of the frontal and temporal lobes of the brain and is the second most common type of dementia for people older than 65; the C9orf72 mutation is also the most common genetic causes for FTD. The C9orf72 mutation is also found to contribute to Alzheimer?s disease and Huntington?s disease. Despite intense efforts and rapid advances, our understanding of the disease mechanisms and treatment strategies for C9orf72-linked ALS/FTD are still at the early stages. To help relieve the public health burden associated with these diseases, it is important to understand the mechanisms underlying the pathogenesis. We have recently discovered that C9orf72 plays an important role in the regulation of autophagy and related metabolic processes, suggesting that further studies of C9orf72 functions could shed light on the mechanism of ALS/FTD pathogenesis. The goal of the proposed project is to elucidate the mechanisms through which dysregulation of C9orf72 functions leads to molecular defects and neuronal toxicity. The specific aims are to identify the central mechanisms through which C9orf72 regulates autophagy and related metabolism, to delineate the pathways through which the pathogenesis is generated, and to identify potential intervention strategies. The proposed studies, which combine biochemical, molecular, and genetic approaches, are expected to provide insight into fundamental mechanisms of neurodegeneration in ALS/FTD that may ultimately leads to novel approaches for treating these devastating neurodegenerative diseases.